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Subject[PATCH 1/5] kasan: detect invalid frees for large objects
Date
Detect frees of pointers into middle of large heap objects.

I dropped const from kasan_kfree_large() because it starts propagating
through a bunch of functions in kasan_report.c, slab/slub nearest_obj(),
all of their local variables, fixup_red_left(), etc.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Cc: kasan-dev@googlegroups.com
---
include/linux/kasan.h | 4 ++--
lib/test_kasan.c | 33 +++++++++++++++++++++++++++++++++
mm/kasan/kasan.c | 12 +++++-------
mm/kasan/kasan.h | 3 +--
mm/kasan/report.c | 3 +--
mm/slub.c | 4 ++--
6 files changed, 44 insertions(+), 15 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index e3eb834c9a35..fc9e642533f8 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -56,7 +56,7 @@ void kasan_poison_object_data(struct kmem_cache *cache, void *object);
void kasan_init_slab_obj(struct kmem_cache *cache, const void *object);

void kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags);
-void kasan_kfree_large(const void *ptr);
+void kasan_kfree_large(void *ptr);
void kasan_poison_kfree(void *ptr);
void kasan_kmalloc(struct kmem_cache *s, const void *object, size_t size,
gfp_t flags);
@@ -108,7 +108,7 @@ static inline void kasan_init_slab_obj(struct kmem_cache *cache,
const void *object) {}

static inline void kasan_kmalloc_large(void *ptr, size_t size, gfp_t flags) {}
-static inline void kasan_kfree_large(const void *ptr) {}
+static inline void kasan_kfree_large(void *ptr) {}
static inline void kasan_poison_kfree(void *ptr) {}
static inline void kasan_kmalloc(struct kmem_cache *s, const void *object,
size_t size, gfp_t flags) {}
diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 2724f86c4cef..e9c5d765be66 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -94,6 +94,37 @@ static noinline void __init kmalloc_pagealloc_oob_right(void)
ptr[size] = 0;
kfree(ptr);
}
+
+static noinline void __init kmalloc_pagealloc_uaf(void)
+{
+ char *ptr;
+ size_t size = KMALLOC_MAX_CACHE_SIZE + 10;
+
+ pr_info("kmalloc pagealloc allocation: use-after-free\n");
+ ptr = kmalloc(size, GFP_KERNEL);
+ if (!ptr) {
+ pr_err("Allocation failed\n");
+ return;
+ }
+
+ kfree(ptr);
+ ptr[0] = 0;
+}
+
+static noinline void __init kmalloc_pagealloc_invalid_free(void)
+{
+ char *ptr;
+ size_t size = KMALLOC_MAX_CACHE_SIZE + 10;
+
+ pr_info("kmalloc pagealloc allocation: invalid-free\n");
+ ptr = kmalloc(size, GFP_KERNEL);
+ if (!ptr) {
+ pr_err("Allocation failed\n");
+ return;
+ }
+
+ kfree(ptr + 1);
+}
#endif

static noinline void __init kmalloc_large_oob_right(void)
@@ -505,6 +536,8 @@ static int __init kmalloc_tests_init(void)
kmalloc_node_oob_right();
#ifdef CONFIG_SLUB
kmalloc_pagealloc_oob_right();
+ kmalloc_pagealloc_uaf();
+ kmalloc_pagealloc_invalid_free();
#endif
kmalloc_large_oob_right();
kmalloc_oob_krealloc_more();
diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 8aaee42fcfab..ecb64fda79e6 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -511,8 +511,7 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object)

shadow_byte = READ_ONCE(*(s8 *)kasan_mem_to_shadow(object));
if (shadow_byte < 0 || shadow_byte >= KASAN_SHADOW_SCALE_SIZE) {
- kasan_report_double_free(cache, object,
- __builtin_return_address(1));
+ kasan_report_invalid_free(object, __builtin_return_address(1));
return true;
}

@@ -602,12 +601,11 @@ void kasan_poison_kfree(void *ptr)
kasan_poison_slab_free(page->slab_cache, ptr);
}

-void kasan_kfree_large(const void *ptr)
+void kasan_kfree_large(void *ptr)
{
- struct page *page = virt_to_page(ptr);
-
- kasan_poison_shadow(ptr, PAGE_SIZE << compound_order(page),
- KASAN_FREE_PAGE);
+ if (ptr != page_address(virt_to_head_page(ptr)))
+ kasan_report_invalid_free(ptr, __builtin_return_address(1));
+ /* The object will be poisoned by page_alloc. */
}

int kasan_module_alloc(void *addr, size_t size)
diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 7c0bcd1f4c0d..57f517d1dfce 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -107,8 +107,7 @@ static inline const void *kasan_shadow_to_mem(const void *shadow_addr)

void kasan_report(unsigned long addr, size_t size,
bool is_write, unsigned long ip);
-void kasan_report_double_free(struct kmem_cache *cache, void *object,
- void *ip);
+void kasan_report_invalid_free(void *object, void *ip);

#if defined(CONFIG_SLAB) || defined(CONFIG_SLUB)
void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache);
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index eff12e040498..55916ad21722 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -326,8 +326,7 @@ static void print_shadow_for_address(const void *addr)
}
}

-void kasan_report_double_free(struct kmem_cache *cache, void *object,
- void *ip)
+void kasan_report_invalid_free(void *object, void *ip)
{
unsigned long flags;

diff --git a/mm/slub.c b/mm/slub.c
index 3530b3c60ad6..67c8cee43cf6 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1354,7 +1354,7 @@ static inline void kmalloc_large_node_hook(void *ptr, size_t size, gfp_t flags)
kasan_kmalloc_large(ptr, size, flags);
}

-static inline void kfree_hook(const void *x)
+static inline void kfree_hook(void *x)
{
kmemleak_free(x);
kasan_kfree_large(x);
@@ -3911,7 +3911,7 @@ void kfree(const void *x)
page = virt_to_head_page(x);
if (unlikely(!PageSlab(page))) {
BUG_ON(!PageCompound(page));
- kfree_hook(x);
+ kfree_hook(object);
__free_pages(page, compound_order(page));
return;
}
--
2.15.1.620.gb9897f4670-goog
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